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Before making a selection, we must understand several basic concepts regarding vacuum pumps. Vacuum level: The degree of thinness of the gas in a vacuum state, usually expressed as a vacuum level. The value read from the vacuum gauge is called the degree of vacuum. The vacuum degree value represents the extent to which the actual pressure in a system is lower than atmospheric pressure. The value shown on the gauge is referred to as gauge pressure; in the industry, it is also called absolute relative pressure. That is: Vacuum degree = Atmospheric pressure – Absolute pressure (the atmospheric pressure is typically taken as 101325 Pa, while the maximum absolute pressure for water ring vacuum pumps is 3300 Pa) ； The ultimate absolute pressure of a rotary vane vacuum pump is approximately 10 Pa. Ultimate relative pressure: Relative pressure refers to the amount by which the internal pressure being measured is lower than the \"atmospheric pressure\". It indicates that the actual system pressure is lower than the atmospheric pressure. Since the air inside the container is evacuated, the pressure inside remains always lower than the pressure outside the container. Therefore, when expressed in terms of relative pressure or gauge pressure, a negative sign must be placed in front of the value to indicate that the pressure inside the container is lower than the external pressure. Limiting absolute pressure: Absolute pressure refers to the amount by which the measured internal pressure is higher than the \"theoretical vacuum\" (the pressure of theoretical vacuum is 0 Pa). The object it compares against is the absolute vacuum pressure value of the theoretical state. Due to limitations in the manufacturing process, it is impossible for us to reduce the internal pressure to an absolute vacuum level of 0 Pa; as a result, the vacuum level achieved by the vacuum pump is higher than the theoretical vacuum level. So when expressed in absolute vacuum, there is no negative sign in front of the value. Pumping volume: The pumping volume is a factor that measures the pumping speed of a vacuum pump. Typically, units are expressed in L/S and m3/h. It is a parameter to compensate for the air leakage rate. It is easy to understand why, in theory, when using a container of the same volume, a vacuum pump with a high pumping capacity can easily achieve the desired vacuum level, while one with a low pumping capacity does so slowly or even fails to reach that level. This is because it is impossible for pipelines or containers to be completely airtight; a vacuum pump with a high pumping capacity compensates for the drop in vacuum level caused by leaks, allowing it to easily reach the desired vacuum level. It is recommended that, once the theoretical pumping volume has been calculated, we choose a vacuum pump with a higher pumping capacity as much as possible. The specific formula for calculating the exhaust volume will be introduced below. Once we understand the basic parameters of vacuum pumps such as vacuum degree, absolute pressure, and relative pressure, we can proceed with the actual selection of a vacuum pump. 1. Vacuum level required by the process: The operating pressure of the vacuum pump should meet the requirements of the process; when selecting a pump, its vacuum level should be half to one order of magnitude higher than that of the vacuum equipment used in the process. (For example: if the vacuum process requires a vacuum level of 100 Pa (absolute pressure), the vacuum pump selected should be capable of achieving a vacuum level of at least 50 Pa to 100 Pa.) Generally, if an absolute pressure higher than 3300 Pa is required, a water ring vacuum pump is preferred as the vacuum device; if the required absolute pressure is below 3300 Pa, a water ring vacuum pump cannot be used, and instead a rotary vane vacuum pump or a vacuum pump with a higher vacuum level should be chosen as the vacuum generation device. 2. Exhaust volume (exhaust rate) required by the process: The vacuum pump is required to have a certain exhaust rate – that is, the ability to remove gases, liquids, and solids at its operating pressure. The common units for this are m3/h, L/S, and m3/min. For the specific calculation method, you can refer to the formula below to perform the calculations and make the selection on your own. Of course, the selection of a vacuum pump is a comprehensive process that involves factors such as relevant experience. S = (V/t) × ln(P1/P2), where: S is the pumping speed of the vacuum pump (L/s); V is the volume of the vacuum chamber (L); t is the time required to achieve the desired vacuum level (s); P1 is the initial pressure (Pa); P2 is the desired pressure (Pa). 3. Determining the composition of the substance to be evacuated: First, it is necessary to determine whether the substance to be evacuated is a gas, a liquid, or particles. If the gas contains water vapor or small amounts of particulate matter and dust, it is advisable to use a rotary vane vacuum pump with caution. If a higher level of vacuum is required, a filtering device must be used to filter the air before employing a rotary vane vacuum pump as a vacuum generation device. Second, it is necessary to determine whether the substance to be evacuated is corroded (acidic or alkaline, what is its pH value?). If gases containing factors such as acid or alkali corrosion or organic corrosion are present, filtering or neutralization treatment is required before a rotary vane vacuum pump can be used. Third, does the substance being pumped pose a contamination risk to rubber or oils? Appropriate vacuum equipment must be selected depending on the medium being pumped. If the gas contains large amounts of vapors, particles, or corrosive gases, it is necessary to consider installing appropriate auxiliary devices in the pump’s intake pipeline, such as condensers and filters (please contact our technical engineers for details). Fourth, does the noise, vibration, and appearance of the vacuum pump have an impact on the factory? Fifth, as the saying goes, you get what you pay for. When purchasing vacuum pumps and vacuum equipment, priority should also be given to factors such as the quality of the equipment, transportation costs, and the expenses associated with its maintenance.